Aspects of this disclosure relate generally to telecommunications, and more particularly to uplink transmissions in an unlicensed or shared spectrum.
Long Term Evolution (LTE) networks are expanding operation in the unlicensed or shared radio frequency (RF) bands for data offload. For example, using carrier aggregation features, LTE networks can operate at higher data rates while using both licensed and unlicensed RF bands. A wireless communication network may be deployed to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within a coverage area of the network. In some implementations, one or more access points (e.g., corresponding to different cells) provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the coverage of the access point(s). In some implementations, peer devices provide wireless connectively for communicating with one another.
A wireless terminal device (also referred to as user equipment or access terminal) that needs to transmit on an unlicensed or shared RF band may also be required to perform a clear channel assessment (CCA) each time before sending an uplink transmission. For example, a device may perform CCA/eCCA to determine whether a channel is clear for transmission. Generally, the CCA procedures may involve monitoring a channel for a CCA duration or time slot, for example 20 microsecond (μs). If the time slot is clear (e.g., the communications medium is available or accessible), the device may begin using the channel. When a channel is not clear, the device may initialize a random backoff counter for the channel. Each time the device detects a clear time slot, the random backoff counter is decremented. When the random backoff counter reaches 0, the device may transmit for a limited transmission opportunity. The duration of the transmission opportunity may be a multiple of the CCA time slot duration. During the transmission opportunity, other devices would be blocked by the transmission from also transmitting using the same channel.
Methods are needed to provide efficient and improved uplink transmissions among multiple access terminals associated with the same access point, in particular, when such access terminals are contending for access on the uplink channels. For example, it may be desirable to minimize interference at a UE with uplink transmissions caused by another UE's uplink transmissions. One such cause could be a UE sending a beacon signal in advance of the data transmission when reserving the uplink channel. While the network can use uplink grants to UEs to control scheduling of uplink resource blocks to avoid collisions of data transmissions, the network cannot control a UE from sending a reservation beacon signal in an uplink transmission that may happen to interfere with the uplink data transmission by another UE as assigned by an uplink grant.